Definitely not new or a special 'technique'
gardeners/landscapers have been transplanting trees during the bareroot period for decades. I took this and applied it to trees in pots with not much issues. I do the spring stuff too. however, our springs are so unpredictable now, you can never know what to expect afterwards. A lot of folk tend to disregard constantly changing weather conditions, when dishing out the same advice.
Not disregarding changing weather conditions at all. Far from it. Those changes are easier to deal with in the spring than they are in the fall.
For instance, we've been getting substantially "front loaded" winters in the last few years, with early plunges in temps to the low 20s (-6 to - 3 or so) for prolonged periods by Thanksgiving. I have to protect things much sooner than usual. There is nothing I can really do beyond mulching trees into garden beds. That kind of deep cold affects roots in the mulch if it sticks around for more than a couple of nights. Cut roots, or new roots, that freeze are dead roots. That cold continues for months. Those cold snaps are the BEGINNING not the end, of winter.
In the Spring, we also get late freezes and frosts--from some FB post records, I have seen frost as late as the third week in May. Farther north, frost can continue into June. While those late cold snaps are dangerous, I simply bring trees inside until they pass and they do pass within days or weeks, not months.
The U.K. is warmed by the Gulf Stream. Many of us don't have that luxury. We have continental climates, not maritime--moist and relatively warm. We have extremes in heat, cold, precipitation (too much, not enough) and storms (hurricanes, tornados, etc). Those of us in continental climates deal with constant changes.